Angular Dependence in Infrared Linear Dichroism: A Reevaluation of the Theory

Abstract

Parameters such as the viewing angle and the extinction ratio (the ratio of the transmitted light over the total light intensity that reaches the sample) are very important in the design of novel optical devices such as new types of polarizers, liquid crystal displays, etc. The initial aim of this work was the comparison of experimentally obtained results to the currently accepted theoretical model that is based on Zbinden's theory of intensity ellipsoid. Due to observed discrepancies between the above theory and experimental data, a new mathematical model was generated in order to adequately explain the experimental results. This new theory allows the calculation of light absorbance at every combination of azimuthal and tilt angles in complete agreement with the experimentally determined values. In addition, in this paper we settle, once and for all, the confusion that exists in the spectroscopic literature with regard to the dependence of absorption and transmission values vis-à-vis the angle of incidence of the incoming light. We conclusively show that it is absorptance (α) and not absorption or absorbance ( A) which shows a cos2 dependence on the angle formed by the electric vector and the dipole.